FIG. 1 shows a structure of an Optical Burst Switching (OBS) network, where the OBS network is composed of an edge router and a core router. The edge router is adapted to encapsulate input IP packets into a burst, and schedule the generated burst onto an output wavelength. The core router is adapted to switch the corresponding optical burst from an input port to a proper output port according to the information carried in a Burst Header Packet (BHP). Moreover, the core router is also adapted to handle contention between optical bursts in order to accomplish high switching throughput. The core router receives the BHPs which arrive first before forwarding the optical burst. The information carried in the BHP decides the features of the optical burst from the port, for example, arrival time, duration (burst length), port and wavelength information, priority, and so on. The core router processes the BHPs that come from all ports, and determines the configuration state of the optical switching array dynamically in time, so as to send as many burst packets as possible to the expected output port.
The features of the optical burst switching network decide if optical bursts contention exists. When multiple optical bursts contend for the same wavelength of the same output port at the same time, conflict occurs. Contention between optical bursts leads to network congestion and massive data loss. The practicability of the optical burst switching technology depends on the solution to avoiding or reducing the data loss caused by burst contention in the network.
In a traditional electrical switching network, the solution to conflict depends on the electronic buffer. In an optical domain, however, the precisely-termed random storage mechanism does not exist. Currently, the buffer in the optical domain depends on a Fiber Delay Line (FDL). In the prior art, an FDL may be configured on the core router to reduce burst conflicts. Because the signal quality and physical space are limited, the size of the FDL buffer is limited. Moreover, the FDL introduces power loss. If an optical signal amplifier is used to compensate for the power, noise is increased. If optical signals are regenerated, the cost is too high.
In the case that the FDL is lacking or unavailable in the core router, packet loss occurs if the quantity of simultaneously transmitted optical bursts exceeds the quantity of available wavelength channels. In the prior art, a Burst Overlap Reduction Algorithm (BORA) is used to reduce loss of bursts. The principles of the BORA are: The burst into the OBS network is delayed to some extent through an electrical buffer on the edge router to minimize the overlap of bursts and reduce the probability of conflict on the downstream core router. FIG. 2 shows how to delay a burst through the BORA in the prior art, where (a) shows the burst transmission not based on the BORA and (b) shows the burst transmission based on the BORA. In FIG. 2, each core router has two input paths “X” and “Y” and one output path “Z”, and each path has one control channel and two data channels. As shown in (a), if no BORA is applied, four bursts in four data channels of the time (t1, t2) input path are overlapped, with the overlap being 4. As shown in (b), after the BORA is applied, the burst is delayed to some extent, thus reducing the overlap. However, the primary function of the BORA is to apply the scheduling technology to the edge router, without bringing the core router into full play.